Address translation equipment, terminal equipment and mobile communication method

ABSTRACT

A packet sent in a mobile IP communication between different regions passes through a particular address translation unit, so that the communication route cannot be optimized. The packet cannot be delivered to a mobile node not having a fixed home address. To overcome the difficulties, the address translation unit includes a function to process the mobile IPv6 protocol. The mobile node includes a function to dynamically acquire a home address. A first network and a second network each identify the mobile node by a SIP (session initiation protocol) identifier. The mobile node acquires a home address on the second network and registers a corresponding relation between the identifiers and the home address thereof. A terminal on the second network acquires the home address of the mobile node from information of the mobile node registered to the SIP server according to a SIP procedure.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of nonprovisional U.S. applicationSer. No. 10/330,306 filed on Dec. 30, 2002. Priority is claimed based onU.S. application Ser. No. 10/330,306 filed on Dec. 30, 2002, whichclaims the priority of Japanese Application 2002-156642 filed on May 30,2002, all of which is incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method of providing mobilecommunication by interconnecting a network conforming to a protocol to anetwork conforming to the protocol or another protocol.

In recent years, there has been an animated discussion aboutintroduction of an internet protocol (IP) to a mobile communicationnetwork. The internet engineering task force (IETF) is making efforts tostandardize mobile IPv6. A network of the mobile IPv6 includes a mobilenode (MN), a home agent (HA), and a correspondent node (CN).

A unique IP address (home address) is assigned to each mobile node, theIP address being kept unchanged regardless of movement of the mobilenode. A link having a prefix equal to a prefix of the home address iscalled a home link. When the mobile node moves to or visits a link otherthan the home link, the mobile node obtains an IP address in the visitedlink. This address is called a care-of address (C/O address).

The home agent maintains a binding cache, i.e., a pair of a home addressof a mobile node and a C/O address thereof.

When a mobile node detects a movement, the mobile node sends a controlsignal (binding update) to the home agent to request update of thebinding cache. Having received the control signal (binding update), thehome agent multicasts a message (gratuitous neighbor advertisement) tocapture or to acquire a packet addressed to a mobile node existing onother than the home link. The home agent serves as a proxy of the mobilenode.

The correspondent node (CN) is a node to communicate with the mobilenode. According to the mobile IPv6 specifications, since the mobile nodesends a mobile IPv6 message to the correspondent node, the correspondentnode must also conform to the mobile IPv6.

Description will now be given of a procedure for the correspondent nodeto transmit a packet to the mobile node.

The correspondent node sends a packet addressed to the mobile node tothe home address. The home agent intercepts the packet addressed to thehome address. The home agent retrieves the binding cache according tothe home address of the mobile node and obtains the C/O address of themobile node. The home agent adds to the received packet a header to sendthe packet to the C/O address (encapsulation of the packet). The homeagent then transmits the packet to the mobile node.

Having received the packet, the mobile node removes the headerbeforehand added to the packet (decapsulation of the packet) to restorethe original IP packet.

On receiving the packet thus encapsulated, the mobile node retrieves abinding update list of the mobile node using the IP address of thecorrespondent node. The binding update list includes information ofbinding update message destinations.

When the binding update list does not include an entry for thecorrespondent node, the mobile node sends a control signal (BindingUpdate) to the correspondent node to notify the C/O address of themobile node.

Having received the binding update message from the mobile node, thecorrespondent node registers a pair of the home address and the CIOaddress of the mobile node to the binding cache of the correspondingnode. Thereafter, the correspondent node directly sends the packet tothe C/O address of the mobile node for route optimization. In the IPheader of the packet, the C/O address of the mobile node and the homeaddress thereof are set to a source address field and an IPv6 routingheader field, respectively.

On the other hand, with rapid spread of IP networks, the technique tointerconnect areas or domains of mutually different address systems toeach other becomes more important.

For example, a method (IETF RFC1631) using a network address translator(NAT) is known as a technique to interconnect a network conforming to aprivate address to a network conforming to a public address.

The network address translator conducts translation between a privateIPv4 address and a public IPv4 address. The basic network addresstranslator changes the source or destination address when a datagrampasses the translator (NAT) between two areas connected to each other byan NAT router. When an address space of the private network collideswith an address space of the public network, a twice NAT technique isoften employed to solve the address collision. The twice NAT techniquechanges the source and destination addresses when a datagram passes thetwice network address translator (NAT) between two areas connected toeach other by a twice NAT router.

To solve the address collision, the twice NAT operates as follows. Toinitiate communication with Host-X in the public area, Host-A in theprivate area sends a query packet for a domain name system (DNS) addressof Host-X. A domain name service-application level gateway (DNS-ALG)acquires the query packet, and translates an address for Host-x to anaddress (Host-X PRIME) routable in the private area, and then returnsthe packet to Host-A. When the DNS address resolution is finished,Host-A starts communication with Host-X PRIME. At a point of time whenthe packet passes the twice NAT, the source address is translated intoan address that the NAT has and the destination address is translatedinto Host-X. Similar translation is conducted also for a response packetfrom Host-X. IETF RFC2694 describes operation of the DNS-ALG in detail.

This example is a technique used when a network to which a firstterminal belongs and a network to which a second terminal communicatingwith the first terminal belongs conform to the same communicationprotocol. When the communication protocol differs between the networks,for example, when a network (IPv4 network) conforms to IPv4 and anetwork (IPv6 network) conforms to internet protocol version 6 (IPv6),the translation to interconnect the networks to each other is conductedusing the known methods such as NAT-PT (IETF RFC2766), and SOCKS64 (IETFRFC3089).

In these methods, the format of the IP packet is translated between IPv4and IPv6. For example, the address translation is conducted between IPv4and IPv6. A system to conduct the translation will be referred to as atranslator hereinbelow. For the translation, it is required tobeforehand create a correspondence between IPv4 addresses and IPv6addresses. The correspondence is kept stored in the translator. When thecorrespondence is dynamically created each time a communication takesplace, name resolution of a domain name system (DNS) is used in aninitial step of the creation.

The domain name system is a system to translate a name (characterstring; fully qualified domain name (FQDN)) easily understood by a humansuch as a uniform resource locator (URL) of the web into an IP address.An operation to translate a name into an IP address will be referred toas name resolution hereinbelow. Today, almost all applications on theinternet acquire an IP address of its communicating party or partnerusing the domain name system.

To start communication, the network address translator and the protocoltranslator continuously monitor DNS messages communicated beforestarting the communication, using the fact described above. Thetranslator uses a query message for name resolution as a trigger tocreate translation information (such as a correspondence of IPaddresses). Specifically, when an IPv6 terminal conducts name resolutionfor a name and a response thereto is an IP address of IPv4, the IPv4terminal translates the IPv4 address into an IPv6 address and sends theIPv6 address to the IPv6 terminal. The IPv4 terminal establishes acorrespondence between the IPv4 address before translation and the IPv6address after translation. That is, the gateway (DNS-ALG) acquires theresponse message of name resolution to dynamically create translationinformation on the basis of the information items before and aftertranslation.

A technique to transmit voice and sound via IP networks has beenenthusiastically discussed today. Voice over internet protocol (VoIP) isa technique to transmit audio information via IP networks. The protocol(VoIP) first sets a temporary speech channel path (session) between twocommunication units or devices. Audio data configured in an IP packet istransferred through the communication path or route thus prepared. Asession control protocol is required to control operation to establish asession between the communication units, to keep the session, and todisconnect the session.

The internet engineering task force (IETF) has stipulated specificationsof a session initiation protocol (SIP; IETF RFC2543) to establish and toterminate a session for IP multimedia communication. The protocol (SIP)attracts attention as a VoIP session control protocol because of itshigh expandability of functions.

The session initiation protocol is an application protocol using atransport mechanism such as a transmission control protocol (TCP) and auser datagram protocol (UDP). The session initiation protocol is atext-based protocol and includes a header to transport a request or aresponse and a message body in which the contents of the session aredescribed. For example, a session description protocol (SDP; IETFRFC2327) is used to describe the SIP session.

The session initial protocol uses architecture of a client-server model.The source client sends a SIP request to a proxy (a SIP server) of thedestination client. The SIP server conducts address resolution of thedestination of communication using the domain name system (DNS) or thelike to establish a session between the terminals.

The SIP server is in a proxy mode or a redirect mode according to itsfunction. The proxy mode is a method in which a proxy server mediates asession establishing request between a source client and a destinationclient. The redirect mode is a method in which the source clientdirectly connects with the destination client using information of thedestination obtained from a SIP redirect server.

Description will next be given of a SIP connection procedure using a SIPserver in the proxy mode. When a terminal x on an IP network initiatesaudio communication with a terminal y using the session initiationprotocol, the terminal x sends a call setting request (INVITE) to theSIP server. The SIP server determines location information of theterminal y and sends a call setting request thereto. The terminal ysends a response indicating reception of the call. The response is sentto the terminal x via the SIP server through which the call settingrequest has passed. The terminal x sends an ACK request to the terminaly to confirm reception of the response. The ACK request is transferredby the SIP server or is directly sent to the terminal y. As a result,the terminal x can communicate with the terminal y. Ordinarily, a callsetting request and a response thereto include information (sessiondescription) to transfer user information (an audio packet) between theterminals x and y. The session description protocol or the like is usedto prepare the session description. The terminal x (y) sends the userinformation to a destination specified by the terminal y (x).

The session initiation protocol identifies the communicating party usinga SIP uniform resource identifier (SIP URI). A SIP client resisterslocation information to a registrar server. For example, an IP addressis set as the location information. The registrar server sends thelocation information to a location server. The location server keeps acorrespondence between SIP URI and the location information. Theregistrar server and the location server may be installed in the SIPserver.

According to SIP and SDP specifications, information items of a terminaland a SIP server can be specified by IP addresses.

International telecommunication uniorn-telecommunication sector (ITU-T)has standardizes the ITU-T recommendation H.323 stipulating an encodingmethod and a call control method to handle audio and video informationon a network, for example, the internet and a local area network (LAN)on which a bandwidth is not guaranteed. The recommendation H.323 isprepared for packet-based multimedia communication systems and areapplicable to the protocol (VoIP). An H.323 system mainly includes aterminal, a gateway, and a gatekeeper. The gatekeeper has an addresstranslation function and a bandwidth management function for a terminaland a gateway to access a local area network. Messages and protocols forthe call control method and a data transfer method are standardized bythe ITU-T recommendations H.225 and H.245.

The recommendation H.323 identifies a terminal by an alias address. Thegatekeeper manages information of correspondence between alias addressesand transport addresses. For example, an IP address is set to thetransport address.

With spread of the VoIP service, the internet engineering task force andITU-T are discussing assignment of a telephone number (E.164 number orthe like) to a VoIP terminal. An ENUM domain name system (DNS)establishes a correspondence between a telephone number and a uniformresource identifier (URI; SIP URI, H.323 alias address, etc.) The system(ENUM DNS) is based on the DNS architecture and protocol and isstipulated by RFC2916. A node to issue a query to the ENUM DNStranslates a telephone number into an FQDN format and sends the query tothe ENUM DNS. The ENUM DNS translates information of the FQDN into auniform resource identifier beforehand registered on the destinationside.

SUMMARY OF THE INVENTION

When address translation equipment or an address translation unitinterconnects an area A to an area B and a first terminal belonging tothe area A communicates with a second terminal belonging to the area B,an address translation unit through which a first packet passes managesa correspondence of addresses between the areas A and B. Therefore,after the first and second terminals start communication, any packetcommunicated therebetween passes through the address translation unit.

For example, after the communication is started, a route optimizationrequest transmitted from a mobile node (MN) conforming to the mobileIPv6 to a terminal conforming to IPv4 passes through a particularaddress translation unit. This consequently leads to a problem. That is,when the mobile node exists in other than the home link, it isimpossible to optimize the route between the mobile node and the IPv4terminal.

In the IPv4 address system today, almost all terminals for consumers areeach dynamically assigned with an IP address by an internet serviceprovider (ISP). However, when a home address is dynamically assigned tothe mobile node, there arises a problem that a packet addressed to themobile node cannot be appropriately delivered thereto.

The IPv4 addresses are less in number than the IPv6 addresses. Thisresults in a problem. When the number of mobile nodes to communicatewith IPv4 terminals increases, the IPv4 addresses for the addresstranslation unit to create address translation entries becomeinsufficient.

It is therefore an object of the present invention to provide a mobilecommunication system in which when a terminal x belonging to an area Acommunicates with a terminal y belonging to an area B, routeoptimization can be conducted between the terminals x and y even if anaddress system of the area A differs from an address system of the areaB.

Another object of the present invention is to provide a mobilecommunication system in which even if a home address is dynamicallyassigned to a mobile node, a packet can be delivered to the mobile node.

Another object of the present invention is to provide a mobilecommunication system in which when an address translation unitinterconnects an area A to an area B and a terminal x belonging to thearea A communicates with a terminal y belonging to the area B, theterminals x and y can communicate with each other even if the number ofaddresses routable in the area B is less than that of addresses in thearea A.

To solve the problem, according to the present invention, at least threemeasures are additionally provided in the protocol translation system ofthe prior art as below.

(1) Each address translation unit includes a part to process a mobile IPprotocol to provide a mobile communication service.

(2) A mobile node conforming to the mobile internet protocol includes apart to dynamically acquire a home address and a part to register, whenthe mobile node acquires a home address, the home address to the addresstranslation unit.

(3) To uniquely identify the mobile node, a SIP identifier (SIP URI) isassigned to the mobile node, and the mobile node includes a part toregister a home address to the SIP server.

(4) The address translation unit may include a part which assigns aprivate address as a routable address in IPv4 to the mobile node andwhich notifies, when the address translation unit notifies addressinformation of the mobile node to a terminal on an IPv4 network,information of the address translation unit together with the privateaddress assigned to the mobile node as well as a part to encapsulate andto decapsulate a packet.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of a communication networkaccording to a first embodiment of the present invention.

FIG. 2 is a diagram showing a packet route when a mobile node conformingto the mobile IPv6 has a fixed home address.

FIG. 3 is a diagram showing a packet route when a mobile node conformingto the mobile IPv6 has not a fixed home address in the communicationnetwork according to the present invention.

FIG. 4 is a block diagram showing a configuration of an addresstranslation unit.

FIG. 5 is a block diagram showing a configuration of a SIP server.

FIG. 6 is a diagram showing a format of an IPv4 packet.

FIG. 7 is a diagram showing a format of an IPv4 packet.

FIG. 8 is a diagram showing a format a SIP message.

FIG. 9 is a diagram showing example 1 of a SIP register message.

FIG. 10 is a diagram showing example 2 of a SIP register message.

FIG. 11 is a diagram showing an example of a router advertisementmessage.

FIG. 12 is a diagram showing an example of a binding update message.

FIG. 13 is a diagram showing an example of a binding acknowledgementmessage.

FIG. 14 is a diagram showing a format of an address query message.

FIG. 15 is a diagram showing a format of an address query responsemessage.

FIG. 16 is a diagram showing a translation information table of theaddress translation unit.

FIG. 17 is a diagram showing example 1 of a SIP information managementtable of a SIP server.

FIG. 18 is a diagram showing example 2 of a SIP information managementtable of a SIP server.

FIG. 19 is a diagram showing a binding cache management table of theaddress translation unit.

FIG. 20 is a sequence chart showing a location registration sequenceaccording to the present invention.

FIG. 21 is a flowchart showing a binding cache creation processingroutine of the address translation unit.

FIG. 22 is sequence chart 1 showing a communication sequence between aterminal and a mobile node according to the present invention.

FIG. 23 is sequence chart 2 showing a communication sequence between aterminal and a mobile node according to the present invention.

FIG. 24 is diagram 1 showing an example of a SIP invite message.

FIG. 25 is a diagram showing an example of a SIP 302 message.

FIG. 26 is diagram 2 showing an example of a SIP invite message.

FIG. 27 is a diagram showing an example of a SIP 200 OK message.

FIG. 28 is a diagram showing an example of a configuration of acommunication network in a second embodiment according to the presentinvention.

FIG. 29 is a block diagram showing a configuration of a gatekeeper inthe second embodiment.

FIG. 30 is a sequence chart showing a location registration sequence inthe second embodiment.

FIG. 31 is a block diagram showing a configuration of an addresstranslation unit in a fourth embodiment according to the presentinvention.

FIG. 32 is sequence chart 1 showing a communication sequence between aterminal and a mobile node in the fourth embodiment.

FIG. 33 is sequence chart 2 showing a communication sequence between aterminal and a mobile node in the fourth embodiment.

FIG. 34 is a diagram showing an example of a SIP 200 OK message in thefourth embodiment.

FIG. 35 is sequence chart 3 showing a communication sequence between aterminal and a mobile node in the fourth embodiment.

FIG. 36 is a diagram showing an example of a SIP invite message in thefourth embodiment.

FIG. 37 is sequence chart 4 showing a communication sequence between aterminal and a mobile node in the fourth embodiment.

FIG. 38 is a sequence chart showing a communication sequence between aterminal and a mobile node in FIG. 2.

DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, description will be given of a firstembodiment according to the present invention.

Description will be given in detail of a representative example in whicha mobile node (MN) conforming to the mobile IPv6 on a visited network ofthe mobile node starts communication with an IPv4 terminal.

FIG. 1 shows an example of a communication network in which the mobilenode communicates with the IPv4 terminal according to the presentinvention. The communication network includes networks 7 and 8. In theembodiment, the networks 7 (7 a, 7 b) are mobile IPv6 networks and thenetwork 8 is an IPv4 network. Address translation units (TR) 1 (1 a, 1b) respectively interconnect the networks 7 with the network 8.

The mobile IPv6 network 7 a includes a SIP servers 5 a and a DNS server6 a, and the mobile IPv6 network 7 b includes a SIP servers 5 b and aDNS server 6 b. A mobile node 3 is a mobile node conforming to themobile IPv6.

The network 8 includes a SIP server 5 c, a DNS server 6 c, and aterminal 4.

The address translation unit 1 includes a mobile IPv6 message processingfunction, a function to conduct address translation between IPv4 andIPv6 addresses, a unit to communicate with a SIP application levelgateway (SIP-ALG) 2, and a unit to communicate with a DNS applicationlevel gateway (DNS-ALG) 9.

FIG. 4 shows an example of the address translation unit 1. The unit 1includes interface units (IF; 19 a, 19 b, . . . , 19 n) to accommodatecommunication lines (18 a, 18 b, . . . , 18 n), a packet transfer, aprocessing group 14, and a packet transfer control group 13.

The packet transfer, processing group 14 includes a distributionprocessing part 15, a translation information memory part 16, and apacket translation, processing part 17. The distribution processing part15 includes a function to detect a SIP message, a DNS message, and amobile IP message. The translation information memory part 16 includes atranslation information table 500 to store information necessary foraddress translation. The packet translation, processing part 17 includesa function to translate a data packet.

FIG. 16 shows an example of a table configuration of the translationinformation table 500. The table 500 stores a correspondence between anIPv4 address 501 and an IPv6 address 502.

When an IPv4 (IPv6) packet is received, the packet translation,processing part 17 makes a search through the translation informationmemory part 16 to translate an IPv4 (IPv6) address into an IPv6 (IPv4)address. In the operation, the part 17 also translates variousinformation other than the IP address.

FIG. 6 shows a format of an IPv4 packet and FIG. 7 shows a format of anIPv6 packet.

In the address translation, not only the IP address but also the formatis also translated.

Returning to FIG. 4, the address translation unit 1 will be described.

The packet transfer control group 13 includes a translation entryregistration processing part 11, a translation entry creation processingpart 12, and a mobile IP message processing part 20.

The translation entry registration processing part 11 registerstranslation information to the translation information memory part 16.

The translation entry creation processing part 12 includes an addresspool to translate an IPv6 (IPv4) address into a routable address on anIPv4 (IPv6) network and a function to create address translationinformation.

The mobile IP message processing part 20 includes a mobile IP protocolprocessing function, a home agent (HA) function, a binding cachemanagement table 310, and a binding update processing routine 60.

FIG. 19 shows an example of a table layout of the binding cachemanagement table 310. The table 310 relates a home address 311 to a C/Oaddress 312, a lifetime 313, an HR flag 314, a proxy flag 315, a homeaddress routing prefix length 316, a sequence number 317, a securityassociation (BSA) 318, and a dynamic flag 319.

FIG. 5 shows a configuration example of the SIP server 5. The server 5includes interface units (IF) 33 (33 a, 33 b) to respectivelyaccommodate communication lines 34 (34 a, 34 b), a memory 32, a centralprocessing unit (CPU) 1, and a bus 35 connecting the constituentcomponents to each other.

The memory 32 stores a SIP processing part and a location informationmemory part 37.

The SIP processing part 36 includes a SIP protocol function and a SIPserver function.

The location information memory part 37 includes a registrar serverfunction and a location server function. The location server function ofthe part 37 includes a SIP information management table.

FIG. 17 shows an example of a table configuration of a SIP informationmanagement table 510 of the SIP server 5 a on the network 7 a.

FIG. 18 shows an example of a table configuration of a SIP informationmanagement table 520 of the SIP server 5 b on the network 7 b.

The table 510 (520) stores a correspondence between SIP-URI 511 (521)and location information 512 (522).

FIG. 3 shows a communication route for the terminal 4 on the network 8to communicate with the mobile node 3 having registered its location onthe network 7 b.

Referring to the sequences shown in FIGS. 20, 22, and 23, descriptionwill be given of a communication sequence for the mobile node 3 existingon the network 7 to communicate with the terminal 4 on the network inFIG. 3.

FIG. 20 shows a location registration procedure of the mobile node 3 onthe network 7 b.

Assume that the mobile node 3 dynamically acquires a home address on thenetwork 7 b. Assume also that the mobile node 3 is identified by aSIP-URI (userA@home.com) on the home network 7 a and is identified by aSIP-URI (userA%home.com@visit.com) on the visited network 7 b.

The mobile node 3 moved to the network 7 b receives a routeradvertisement message from the address translation unit (TR) 1 b (101).

FIG. 11 shows a format example 420 of the router advertisement message.The router advertisement message 420 is stored in a payload field 57 ofthe IPv6 packet format shown in FIG. 7.

When an H bit is set to the router advertisement message, the mobilenode 3 regards the message as a router advertisement issued from thehome agent. When an R bit is set to a prefix information option 422, themobile node 3 registers an address contained in the prefix to an HA listas an HA address. The mobile node 3 acquires a prefix of the mobile node3 using a prefix length of the prefix information option 422 and theaddress contained in the prefix to create a home address of the mobilenode 3 (102).

When the H bit is not set to the router advertisement message, themobile node 3 creates a home address of the mobile node 3 using theprefix length of the prefix information option 422 of the routeradvertisement and the address contained in the prefix. Next, the mobilenode 3 retrieves a home agent of the mobile node 3 using a dynamic homeagent discovery function.

Returning to FIG. 20, the communication sequence will be described.Having created the home address, the mobile node 3 sends a message(Binding Update) requesting registration of the home address to theaddress translation unit 1 b having the home agent (HA) function (103).

FIG. 12 shows a format example 430 of the binding update message. AnIPv6 destination options header 431 and an IPv6 mobility header 432 arestored in an extension header 56 of the IPv6 packet format shown in FIG.7.

The binding update message from the mobile node 3 to the addresstranslation unit 1 b contains values as below. The home address createdin step 102 is set to a source IP address 54 of the IPv6 packet header,a home address option of the IPv6 destination options header 431, and ahome address of the IPv6 mobile header 432. A value more than zero isset to a lifetime field of the IPv6 mobile header 432.

Having received the binding update message, the address translation unit1 b activates a binding cache creation processing routine 60 shown inFIG. 21.

FIG. 21 shows the routine 60 in a flowchart. In a state ready to receivethe binding update message (61), the address translation unit 1 bcompares the source IP address of the IPv6 packet containing the bindingupdate message with the home address in the IPv6 destination optionsheader and that contained in the IPv6 mobility header (62). If thesource IP address is equal to the home address, the address translationunit 1 b makes a search through the binding cache management table 310for an entry at the address (63). If the entry is absent, thetranslation unit 1 b examines the lifetime value in the IPv6 mobilityheader (64). If the value is more than zero, the translation unit 1 badds a new entry to the binding cache management table 310 (65, 104).The translation unit 1 b sets “1” to a dynamic field 319 of the newentry. This indicates that the entry belongs to a mobile node of whichthe home address has been dynamically acquired. To the mobile node 3,the translation unit 1 b sends a response (Binding Acknowledgement) tothe binding update message (66, 105) and terminates the routine.

FIG. 13 shows a format example 440 of the binding acknowledgementmessage.

In step 63, if an entry exists at the address in the binding cachemanagement table 310 of the address translation unit 1 b, thetranslation unit 1 b examines the lifetime value of the IPv6 mobilityheader (67). If the value is zero, the translation unit 1 b deletes theentry from the table 310 (68). The translation unit 1 b sends a bindingacknowledgement message to the mobile node 3 (69), deletes the proxyneighbor cache (70), and terminates the routine.

In step 67, if a valid value is set to the lifetime field, the addresstranslation unit 1 b updates the lifetime value of the entry (77). Thetranslation unit 1 b then sends a binding acknowledgement message to themobile node 3 (78) and terminates the routine.

If the binding update message cannot be accepted in step 61, thetranslation unit 1 b sends a binding acknowledgement message includingan error indication to the mobile node 3 and terminates the routine(76).

If the lifetime value is zero in step 64, the translation unit 1 b sendsa binding acknowledgement message to the mobile node 3 and terminatesthe routine (66).

If the source IP address differs from the home address in step 62, theaddress translation unit 1 b searches the binding cache management table310 for an entry at the address (71). If the entry is absent, thetranslation unit 1 b examines the lifetime value of the IPv6 mobilityheader. If the lifetime value is valid, the translation unit 1 b adds anew entry to the table 310 (72). For the new entry, the unit 1 b doesnot set a flag to the dynamic field. To the mobile node 3, thetranslation unit 1 b multicasts a response (binding acknowledgement) tothe binding update message (73). To acquire a packet addressed to thehome address of the mobile node 3, the translation unit 1 b sends agratuitous neighbor advertisement message, creates a proxy neighborcache (74), and terminate the routine.

If the entry exists in step 71 and the received message includes a validlifetime value, the translation unit 1 b updates the lifetime value ofthe entry (75).

Returning to FIG. 20, the communication sequence will be described.

Having received the binding acknowledgement message, the mobile node 3sends a SIP message (register) to the SIP server 5 b on the network 7 bto request registration of location information of the mobile node 3(106).

FIG. 8 shows a protocol stack and a message format of SIP. A packet ofSIP includes an IP header 41, a TCP/UDP header 42, and a payload 43. Thepayload 43 stores information of SIP. The SIP information includes astart-line field 44, a message-header field 45, and a message-body field46. The start line 44 indicates a type and a destination of the SIPmessage. The message header 45 includes a SIP parameter. The messagebody 46 indicates information of a connection logically establishedbetween terminals. The message body is described using, for example, theprotocol (SDP).

FIG. 9 shows a message example 401 of the SIP message (register) fromthe mobile node 3 to the SIP server 5 b. A domain name of the SIP server5 b to conduct registration is set to a start-line field. A to-headerfield indicates an update objective item. A contact-header fieldindicates information to be registered to the registrar server. Themobile node 3 sets to the contact-header field a home address (mn6)acquired on the network 7 b.

Returning to FIG. 20, the communication sequence will be described.Having received the SIP message (register), the SIP server 5 b adds anentry 520-1 to the SIP information management table 520 (107). The entry520-1 keeps a correspondence between the SIP-URI(userA%home.com@visit.com) of the mobile node 3 on the network 7 b andlocation information (userA@mn6) including the home address (mn6)created in step 102. To the mobile node 3, the SIP server 5 b sends aresponse message (200 OK) to the SIP message (register; 108).

The mobile node 3 then transmits an SIR message (register) to the SIPserver 5 a on the home network 7 a to request registration of locationinformation of the mobile node 3 (109).

FIG. 10 shows a message example 402 of the SIP message (register) fromthe mobile node 3 to the SIP server 5 a. In the SIP message 402, theSIP-URI (userA@home.com) of the mobile node 3 on the network 7 a is setto the to-header field and location information of the mobile node 3,i.e., SIP-URI (userA%home.com@visit.com) of the mobile node 3 on thenetwork 7 b is set to the contact-header field.

Having received the SIP message (register), the SIP server 5 a adds anentry 510-1 to the SIP information management table 510 (110). To themobile node 3, the SIP server 5 a sends a response message (200 OK) tothe SIP message (register; 111).

FIGS. 22 and 23 show a procedure for the terminal 4 to transmit a packetto the mobile node 3.

To send a packet to the mobile node 3, the terminal 4 must acquire an IPaddress of the mobile node 3. In the example of this embodiment, theterminal 4 acquires the IP address of the mobile node 3 using a SIPmessage.

Assume that the SIP server 5 c is set to the terminal 4 as a destinationof the SIP message.

The terminal 4 sends a SIP message (invite) to the SIP server 5 c (121).FIG. 24 shows an example of the SIP invite message 403 from the terminal4 to the SIP server 5 c. The SIP message (invite) sets destinationinformation of the invite message to the start-line field. The SIP URI(userA@home.com) of the mobile node 3 is set to the start-line field ofthe SIP message (invite; 121).

Having received the SIP message (invite), the SIP server 5 c determinesthe invite message destination according to destination information ofthe start-line field. If a domain name is set to the destinationinformation, the SIP server 5 c sends a DNS query to the DNS server 6 c.In corporation with the gateway (DNS-ALG) 9 a and the DNS server 6 a,the DNS server 6 c resolves the name of the SIP server 5 a (122). Forexample, an address translation method described in JP-A-2001-274419 isused as the method of corporation of the address translation unit (TR) 1and the gateway (DSN-ALG) 9. The gateway (DSN-ALG) 9 acquires from theaddress translation unit 1 a a temporary IPv4 address corresponding tothe IPv6 address corresponding to the domain name of the SIP server 5 aand translates the DNS query response. The translation information table500 of the translation information memory part 16 in the translationunit 1 a stores the translated information (123, 124).

The SIP server 5 c acquires the temporary IPv4 address of the SIP server5 a as destination information of the SIP message (invite; 124) andsends the message to the temporary IPv4 address (125).

The address translation unit 1 a detects the SIP message (invite; 126)and sends the message to the SIP address translation unit (SIP-ALG) 2 a(127). For example, a SIP message translation method described inJapanese Patent Application Ser. No. 2001-373520 is used as the methodof corporation of the address translation unit (TR) 1 and the gateway(SIP-ALG) 2 a.

From the received SIP message, the gateway (SIP-ALG) 2 a extractsparameters for IP address translation (128). To the address translationunit 1 a, the gateway 2 a sends an address query request 600 includingan IP address of translation parameters (129).

FIG. 14 shows a message format of the address query request 600.

The address translation unit 1 a receives the address query request 600and makes a search through the translation information table 500 of thetranslation entry creation processing part 12 using the IP address oftranslation parameters.

If the IP address is present in the table 500 of the processing part 12,the translation unit 1 a sends an address query request 650 includingthe translated IP address to the gateway 2 a (130).

If the IP address is absent from the table 500 of the processing part12, the translation unit 1 a assigns a routable IP address on thenetwork 7 a to the IP address of translation parameters to create atranslation entry. The translation unit 1 a then activates thetranslation entry registration processing part 11 to set the translationentry to the translation information table 500 of the translationinformation memory part 16. The translation unit 1 a sends an addressquery request response 650 including the translated IP address to thegateway 2 a (130).

FIG. 15 shows a message format of the address query request response650.

The gateway 2 a receives the request response 650 and translates IPaddress information in the SIP message (131).

Having received the SIP message (invite) from the gateway 2 a, theaddress translation unit 1 a translates address information of the IPheader of a packet including the SIP message (invite; 133). Referring tothe translation information table 500 of the translation informationmemory part 16, the translation unit 1 a translates a destinationaddress into a real IPv6 address of the SIP server 5 a and a sourceaddress into a temporary IPv6 address of the SIP server 5 c.

The SIP server 5 a receives the SIP message (invite; 134) and then makesa search through the information management table 510 of the locationinformation memory part 37 using the SIP-URI (userA@home.com) of themobile node 3 set to the start-line field of the message. The SIP server5 a obtains location information (userA%home.com@visit.com) of themobile node 3 (135).

The SIP server 5 a sends a SIP message (302 Moved Temporarily) includingthe location information (userA%home.com@visit.com) of the mobile node 3to the SIP server 5 c (136).

FIG. 25 shows a message example 50 of the SIP message (302 MovedTemporarily) from the server 5 a to the server 5 c. The locationinformation (userA%home.com@visit.com) of the mobile node 3 is set tothe contact header.

Returning to FIG. 22, the communication sequence will be furtherdescribed. In corporation with the gateway 2 a, the address translationunit 1 a translates the IP address of the SIP message (136; 137). Afterhaving translated the address information of the IP header in a packetincluding the SIP message (138), the translation unit 1 a sends the SIPmessage to the SIP server 5 c (139).

Having received the SIP message (302 Moved Temporarily) as a response tothe invite message, the SIP server 5 c sends a response acknowledgementmessage (ACK) to the SIP server 5 a (140). When the message (ACK) passesthrough the address translation unit 1 a, the unit 1 a translates the IPaddress of the SIP message in corporation with the gateway 2 a (141).After having translated the address information of the IP header in apacket including the SIP message (142), the translation unit 1 a sendsthe SIP message to the SIP server 5 a (143).

According to the contact header (userA%home.com@visit.com) of thereceived SIP message (302 Moved Temporarily), the SIP server 5 cdetermines the location information of the mobile node 3.

If a domain name has been set to the location information, the SIPserver 5 c sends a DNS query to the DNS server 6 c. The DNS server 6 cresolves the name of the SIP server 5 b in corporation with a gateway(DNS-ALG) 9 b and the DNS server 6 b (151, 152). The gateway 9 bacquires from the address translation unit 1 b a temporary IPv4 addresscorresponding to an IPv6 address corresponding to the domain name of theSIP server 5 b and translates the DNS query response. The translationinformation is stored in the translation information table 500 of thetranslation information memory part 16 of the translation unit 1 b.

The SIP server 5 c acquires as destination information of the SIPmessage (invite) a temporary IPv4 address of the SIP server 5 b (153)and sends the SIP message (invite) to the temporary IPv4 address (154).

FIG. 26 shows a message example 405 of the SIP message (invite) from theserver 5 c to the server 5 b. The location information(userA%home.com@visit.com) of the mobile node 3 is set to the start-linefield as destination information of the message.

Returning to FIG. 23, the communication sequence will be described. Whenthe SIP message (invite; 154) passes through the address translationunit 1 b, the unit 1 b translates the IP address contained in the SIPmessage in corporation with the gateway 2 b (155). Having translatedaddress information of the IP header of a packet containing the SIPmessage (156), the translation unit 1 b sends the SIP message to the SIPserver 5 b (157).

The SIP server 5 b makes a search through the SIP information managementtable 520 of the location information memory part 37 using the value(userA%home.com@visit.com) set to the star-line field of the SIPmessage. The SIP server 5 b acquires location information (userA@mn6) ofthe mobile node 3 and sends the SIP message (invite) to the mobile node3 (158).

If the SIP message (invite) is acceptable, the mobile node 3 sends a SIPmessage (200 OK) as a response.

According to via-header information set to the SIP message (invite), theSIP message (200 OK) is sent to the terminal 4 via the SIP server havingprocessed the SIP message (invite; 159, 160, 163, 164).

The SIP message (200 OK) is a normal response to the SIP message(invite).

FIG. 27 shows a message example 406 of the SIP message (200 OK) from themobile node 3 to the SIP server 5 b. A value used as destinationinformation by the terminal 4 to send data to the mobile node 3 is setto a c field of the message body. In the embodiment, a home address(mn6) dynamically acquired on the network 7 b by the mobile node 3 isset to the c field.

Returning to FIG. 23, the communication sequence will be furtherdescribed. When the SIP message (200 OK; 160) passes through the addresstranslation unit 1 b, the unit 1 b translates the IP address containedin the SIP message in corporation with the gateway 2 b (161).

Specifically, the gateway 2 b extracts as an IP address of translationparameters the home address (mn6) of the mobile node 3 set to the cfield of the SIP message (200 OK) and transmits an address query requestto the address translation unit 1 b.

The translation unit 1 b makes a search through the translationinformation table 500 of the translation entry creation processing part12 using the IP address of translation parameters.

If the IP address is absent from the table 500 of the processing part12, the address translation unit 1 b assigns a temporary IPv4 address(vmn4) to the home address (mn6) of the mobile node 3. The unit 1 bactivates the translation entry registration processing part 11 toregister a correspondence between the home address (mn6) of the mobilenode 3 and the temporary IPv4 address (vmn4) to the translationinformation table 500 of the translation entry creation processing part12.

The gateway 2 b translates the temporary IPv4 address (vmn4) for thehome address of the mobile node 3 in the c field of the SIP message.

The address translation unit 1 b translates address information of theIP header in a packet containing the SIP message (162) and sends the SIPmessage to the SIP server 5 b.

The terminal 4 receives the SIP message (200 OK) and acquires theaddress (vmn4) of the mobile node 3 from the c field.

Having received the SIP message (200 OK), the terminal 4 sends aresponse confirmation message (ACK) to the mobile node 3 (165, 166).

When the SIP message (ACK; 166) passes through the address translationunit 1 b, the unit 1 b translates the IP address contained in the SIPmessage in corporation with the gateway 2 b (167). After havingtranslated the address information of the IP header in a packetincluding the SIP message (168), the translation unit 1 b sends the SIPmessage to the SIP server 5 b (169). The server 5 b sends the SIPmessage (ACK) to the mobile node 3 (170).

As a result, the procedure sets a logical connection between theterminal 4 and the mobile node 3, that is, the terminal 4 and the mobilenode 3 can communicate with each other.

To the mobile node 3, the terminal 4 sends a packet including thetemporary IPv4 address (vmn4) as a destination address (DA) and the IPv4address (a4) of the terminal 4 as the source address (SA) of the datapacket (171).

According to the translation entry created in step 161, the addresstranslation unit 1 b changes the destination address from the temporaryIPv4 address (vmn4) to the IPv6 address (mn6). The translation unit 1 bassigns the temporary IPv6 address (va6) to the IPv4 address (a4) of theterminal 4 and updates the source address to the temporary IPv6 address(va6; 172).

The translation unit 1 b sends the packet with the updated headerinformation to the mobile node 3 (173).

To sends a packet to the terminal 4, the mobile node 3 uses an ordinaryIPv6 packet transmitting procedure.

Referring to FIGS. 2 and 38, description will be given of a flow of apacket sent from the terminal 4 to the mobile node 3 when the mobilenode has a fixed home address. Assume that the address translation unit1 a has the home agent (HA) function and the terminal identifies themobile node 3 by a name.

FIG. 2 shows a route of a packet when the mobile node 3 has a fixed homeaddress.

FIG. 38 shows a procedure for the terminal 4 to send a packet to themobile node 3 in FIG. 2.

The mobile node 3 detects an event of movement from the network 7 a tothe network 7 b and sends a control signal (Binding Update) to theaddress translation unit 1 a having the home agent function (701). Thecontrol signal includes a home address (mn6) of the mobile node 3 and acare-of (C/O) address acquired on the network 7 b.

Having received the control signal, the translation unit 1 a storesinformation of the mobile node 3 in the binding cache and operates as aproxy of the mobile node 3. The translation unit 1 a sends a responsesignal (Binding Acknowledgement; 702).

The terminal 4 resolves the name of the mobile node 3 using the DNSserver 6 (703 to 707). In step 706, the translation unit 1 a assigns atemporary IPv4 address (vmn4) to the home address (mn6) of the mobilenode to create a translation entry.

The terminal 4 acquires vmn4 as the home address of the mobile node 3and sends a packet to vnm4 (708). When the packet passes through theaddress translation unit 1 a, the unit 1 a translates addressinformation of the IP header in the packet from IPv4 into IPv6 (709).After the address information is translated, the temporary IPv6 address(va6) corresponding to the IPv4 address (a4) of the terminal 4 is set tothe source address in the IP header and the home address (mn6) of themobile node 3 is set to the destination address.

The address translation unit 1 a refers to the binding cache created instep 701 and acquires the care-of address (c/omn6) of the mobile node 3from the home address (mn6) of the mobile node 3. The translation unit 1a encapsulates the translated IPv6 packet according to IPv6 and sendsthe packet to the mobile node 3 (710). The care-of address (c/omn6) ofthe mobile node 3 is set to the destination address of the encapsulationheader and an address (tra6) of the translation unit 1 a is set to thesource address of the encapsulation header.

The mobile node 3 removes the encapsulation header from the receivedpacket to obtain the original packet. The mobile node 3 makes a searchthrough the binding update list thereof using the source address of theoriginal packet. The temporary IPv6 address (va6) of the terminal 4 isbeforehand set to the source address of the original packet.

If the pertinent entry is absent from the binding update list of themobile node 3, the mobile node 3 sends a control signal (Binding Update)to the temporary IPv6 address (va6) of the terminal 4 (711). The controlsignal passes through the address translation unit 1 a. The unit 1 astores the binding cache in place of the terminal 4. Or, the unit 1 atranslates the control signal into the IPv4 format to translate theheader information (712) and sends the control signal to the terminal 4(713).

If “Binding Update” is transmitted to the terminal 4, the terminal 4sends the packet addressed to the mobile node 3 to the temporary IPv4address (vc/omn4) corresponding to the care-of address of the mobilenode 3 (714). The packet passes through the address translation unit 1a. The unit 1 a translates the header (715) of the packet and sends thepacket to the care-of address (c/omn6) of the mobile node 3 (716).

If the address translation unit 1 a stores the binding cache in place ofthe terminal 4, the terminal 4 sends the packet to the mobile node 3 ina procedure similar to that of steps 708 to 710. In place of step 710,the translation unit 1 a may send the packet to the care-of address ofthe mobile node 3. At this point, the packet includes a routing header.The home address of the mobile node 3 is set to the routing header.

As can be seen from the description above, the control signal sent fromthe mobile node 3 to the terminal 4 to optimize the route and the packetsent from the terminal 4 to the mobile node 3 after the routeoptimization pass the address translation unit 1 a. Therefore, when themobile node has a fixed home address, the route between the mobile node3 and the terminal 4 cannot be optimized.

According to the first embodiment of the present invention, by using theaddress translation unit 1 having the mobile IP protocol processingfunction and the SIP server 5, a packet can be delivered to the mobilenode 3 of the mobile IPv6, the node 3 not having a home address. Sincethe packet addressed to the mobile node 3 passes through the addresstranslation unit 1 existing on a network on which the mobile node 3 hasdynamically acquired a home address, the route of the packet to mobilenode 3 can be optimized. By using SIP as the session control procedurebetween the mobile node 3 and the terminal 4, audio signals can becommunicated between the mobile node 3 and the terminal 4.

Referring now to the drawings, description will be given of a secondembodiment of the present invention.

The first and second embodiments differ from each other in the sessioncontrol protocol type and the method of identifying the mobile node.

The second embodiment uses ITU-T H.323 as the session control protocol.The second embodiment identifies the mobile node by an alias addressstandardized in H.323.

FIG. 28 shows a configuration example of a communication network when amobile node conforming to the mobile IPv6 communicates with an IPv4terminal in the second embodiment.

In the second embodiment, an address translation unit 1 includes a unitto communicate with a H.323 address translation unit (H.323-ALG) 10 inplace of the gateway (SIP-ALG) 2 and a unit to detect a H.323 message.

In the second embodiment, networks 7 and 8 each include a gatekeeper 30in place of a SIP server.

The gateway (H.323-ALG) 10 includes (1) a unit to extract a translationparameter(s) address from the H.323 message, (2) a unit to send anaddress translation request to the address translation unit 1, (3) aunit to receive a response to the address translation request from theaddress translation unit 1, and (4) a unit to update the translationparameter(s) address of the H.323 message according to informationreceived from the address translation unit 1.

FIG. 29 shows a configuration example of the gatekeeper 30. The keeper30 includes interface units (IF; 1003 a, 1003 b) to respectivelyaccommodate communication lines (1004 a, 1004 b), a memory 2002, a CPU1001, and a bus 1005 to connect the constituent components to eachother.

The memory 1002 stores a H.323 processing part 1006 and a locationinformation memory part 1007.

The H.323 processing part includes a H.323 protocol function and agatekeeper function.

The location information memory part 1007 includes a table of acorrespondence between H.323 alias addresses and H.323 transportaddresses. In the second embodiment, the mobile node 3 is uniquelyidentified by a H.323. alias address.

FIG. 30 shows a procedure for the mobile node 3 to register a locationon a network 7 b in the second embodiment.

The mobile node 3 dynamically acquires a home address on the network 7b. A procedure from step 101 to step 105 is almost the same as that ofthe first embodiment.

The location registration procedure varies between the second and firstembodiments in the control signal used to register a location to thegatekeeper 30. In the second embodiment, the control signal to registerthe location is a control signal standardized in the ITU-T H.323recommendations.

The mobile node 3 sends a control signal (Registration Request (RRQ)) toa gatekeeper (GK) 30 b to register a location (181). Having received thecontrol signal, the gatekeeper 30 b extracts an H.323 alias address ofthe mobile node 3 from the control signal. The gatekeeper 30 bdetermines a home network 7 a of the mobile node 3 according to theH.323 alias address of the mobile node 3 and sends the control signal toa gatekeeper 30 a (182). The gatekeeper 30 b may also store the locationinformation of the mobile node 3 in the location registration memorypart 1007.

Having received the control signal for the location registration, thegatekeeper 30 a adds an entry of the H.323 alias address of the mobilenode 3 to the location registration memory part 1007 and storesinformation of a correspondence between the H.323 alias address and theH.323 transport address of the mobile node 3 (183). The gatekeeper 30 astores a home address dynamically assigned to the mobile node in a H.323transport address field.

The gatekeeper 30 a sends a response (Registration Confirmation (RCF))to the control signal requesting the location registration via thegatekeeper 30 b to the mobile node 3 (184, 185).

In the second embodiment, a procedure for a terminal 4 to send a packetto a terminal 3 is basically the same as that of the first embodimentexcepting that the SIP message is replaced with the H.323 message.

According to the second embodiment of the present invention, by using anaddress translation unit having the mobile IP protocol processingfunction and a gatekeeper, a packet can be delivered to a mobile node 3conforming to the mobile IPv6, the node 3 not having a home address.Since a packet addressed to the mobile node 3 passes an addresstranslation unit existing on a network on which the mobile node 3 hasdynamically acquired a home address, the route of the packet to themobile node 3 can be optimized. By using H.323 as the session controlprocedure between the mobile node 3 and the terminal 4, audio signalscan be communicated therebetween.

Description will now be given of a third embodiment of the presentinvention. In this embodiment, a telephone number is assigned to amobile IPv6 terminal (mobile node (MN)) on the network shown in thefirst or second embodiment.

In the third embodiment, the networks 7 and 8 each adopt ENUM DNS. TheENUM DNS manages information of a correspondence between telephonenumbers and uniform resource identifiers (SIP-URI, H.323 aliasaddresses, and the like).

To send a packet to the mobile node 3, the terminal 4 specifies themobile node 3 by a telephone number. The terminal 4 issues a query tothe ENUM DNS for a uniform resource identifier (URI) of the mobile node3. After the URI of the mobile node 3 is acquired, the terminal 4executes processing similar to the processing of the first or secondembodiment.

According to the third embodiment of the present invention, if aterminal specifies its communication party by a telephone number andtranslates the telephone number into a uniform resource identifier, itis possible to deliver a packet to a mobile IPv6 terminal not having ahome address.

Description will now be given of a fourth embodiment of the presentinvention by referring to the drawings.

The fourth embodiment has a feature of a packet encapsulation unit inthe IP address translation unit 1.

FIG. 31 shows a configuration example of the address translation unit 1of the fourth embodiment.

In the configuration, a packet transfer processing group 14 includes anencapsulation, decapsulation processing part 21 in addition to theconstituent blocks or parts of the address translation unit 1 of thefirst embodiment.

The encapsulation, decapsulation processing part 21 of the translationunit 1 includes a function to receive an encapsulated packet from aterminal on the network 8 to remove an encapsulation header therefrom(decapsulation) and a function to add a header to a packet(encapsulation) to be sent to a terminal on the network 8.

The translation entry creation processing part 12 of the embodiment hasan IPv4 private address as a temporary address to be assigned to an IPv6address.

FIGS. 32 and 33 show a procedure for the terminal 4 on the network 8 tocommunicate with the mobile node 3 on the network 7 b in the fourthembodiment.

Assume that the mobile node 3 dynamically acquires a home address on thenetwork 7 b and registers a location in a procedure of FIG. 20 for thefirst embodiment.

The communication procedure of the fourth embodiment is the same as thatof the first embodiment up to step 160. Processing varies therebetweenin the processing of step 161 and subsequent steps.

Referring now to FIG. 33, description will be given of the procedurebeginning at step 160.

The address translation unit 1 b detects a SIP message (200 OK) sentfrom the SIP server 5 b to the SIP server 5 c (160) and sends themessage to the gateway (SIP-ALG) 2 b (201).

The gateway 2 b extracts as a translation parameter(s) IP address a homeaddress (mn6) of the mobile node 3 set to the c field of the SIP message(200 OK). The gateway 2 b sends an address query request including thetranslation parameter(s) IP address to the address translation unit 1 b(202).

The translation unit 1 b makes a search through the translationinformation table 500 of the translation entry creation processing part12 using the translation parameter(s) IP address (mn6).

If the IP address is absent from the table 500 of the processing part12, the translation unit 1 b assigns a temporary IPv4 private address(vpmn4) to the home address (mn6) of the mobile node 3. The translationunit 1 b activates the translation entry registration part 11 to set atranslation entry, namely, a correspondence between the home address(mn6) and the temporary IPv4 private address (vpmn4) of the mobile node3 to the table 500 of the processing part 12 (203).

The address translation unit 1 b sends an address query request response650 including the home address (mn6) and the temporary IPv4 privateaddress (vpmn4; 204). A value indicating the IPv4 private address is setto an IP address type (response) field 623 of the response 650.

The gateway (SIP-ALG) 2 b updates the IP address information in the SIPmessage. If the field 623 of the response 650 contains the IPv4 privateaddress, the gateway 2 b translates the translation parameter(s) IPaddress (mn6) into an IP address (vpmn4) after translation and an IPv4global address (trbg4) assigned to the IPv4 interface of the translationunit 1 b.

Having received a SIP message (200 OK) from the gateway 2 b (205), thetranslation unit 1 b translates address information of the IP header ofa packet containing the SIP message (206). Referring to the translationinformation table 500 of the translation information memory part 16, thetranslation unit 1 b translates the destination address into a real IPv4address of the SIP server 5 c and the source address into a temporaryIPv4 address of the SIP server 5 b.

FIG. 34 shows a message example 407 of the SIP message (200 OK) from theaddress translation unit 1 b to the SIP server 5 c. The temporary IPv4address of the mobile node 3 and the IPv4 global address (trbg4) of thetranslation unit 1 b are set to the contact header field and the cfield.

Having received the SIP message (200 OK), the SIP server 5 c (207) sendsthe message to the terminal 4 (208).

The terminal 4 receives the SIP message (200 OK) and acquires theaddress (vpmn4) of the mobile node 3 and the IPv4 global address (trbg4)of the translation unit 1 b from the c field.

The terminal 4 sends a response confirmation message (ACK) via the SIPserver 5 c to the SIP server 5 b (209, 210). When the SIP message (ACK)passes through the address translation unit 1 b, the unit 1 b translatesthe IP address in the SIP message in corporation with the gateway 2 b(211). After having translated address information of the IP header in apacket containing the SIP message (212), the translation unit 1 b sendsthe SIP message (ACK) to the SIP server 5 b (213). The SIP server 5 bthen sends the SIP message (ACK) to the mobile node 3 (214).

Through the procedure, a logical connection is established between theterminal 4 and the mobile node 3, and hence the terminal 4 and themobile node 3 can communicate with each other.

To sends a data packet to the mobile node 3, the terminal 4 sets thetemporary IPv4 private address (vpmn4) corresponding to the home addressof the mobile node 3 to the destination address in the IP packet headerand the IPv4 address (a4) of the terminal 4 to the source address. Theterminal 4 then encapsulates the original packet according to IPv4. Tterminal 4 sets the IPv4 global address (trbg4) of the addresstranslation unit 1 b to the destination address of the encapsulationheader and the IPv4 address (a4) of the terminal 4 to the source address(215) of the encapsulation header.

Having received the encapsulated packet, the translation unit 1 bdeletes the encapsulation header by the encapsulation, decapsulationprocessing part 21 to extract the original packet (216).

Referring to the translation information table 500 of the translationinformation memory part 16, the translation unit 1 b translates the IPheader of the original packet (217). The unit 1 b changes the source IPaddress from the IPv4 address (a4) of the terminal 4 to the temporaryIPv6 address (va6) and the temporary IPv4 private address (vpmn4) of themobile node 3 to the IPv6 address (mn6).

The address translation unit 1 b sends the packet containing translatedheader information to the mobile node 3 (218).

Description will now be given of a procedure of transmitting a packetfrom the mobile node 3 on the network 7 b to the terminal 4 on thenetwork 8 in the fourth embodiment.

FIG. 35 shows a packet translation procedure when the mobile node 3identifies the terminal 4 by a SIP uniform resource identifier (URI).Assume that a correspondence of location information between theterminal 4 and the SIP URI is beforehand registered to the SIP server 5c.

Assume that the mobile node dynamically 3 acquires a home address on thenetwork 7 b and registers a location according to the procedure shown inFIG. 20 for the first embodiment. The mobile node 3 thus acquired thehome address on the network 7 b recognizes that he address translationunit 1 b is a home agent thereof and the mobile node 3 exists on thehome link.

According to the mobile IPv6 specifications, a mobile node existing onthe home link transfers a packet by the ordinary IPv6 routing.Therefore, the mobile node 3 can transfer a packet to the terminal 4using the ordinary IPv6 routing.

To acquire an IP address using the SIP URI of the terminal 4, the mobilenode 3 sends a SIP message (invite) to the SIP server 5 b (251). The SIPURI of the terminal 4 is set as destination information of the invitemessage to the start-line field of the SIP message 251.

The SIP server 5 b sends the SIP message (invite) to the SIP server 5 c(252).

The address translation unit 1 b detects the SIP message (invite) sentfrom the SIP server 5 b to the SIP server 5 c and transmits the messageto the gateway (SIP-ALG) 2 b (253).

The gateway 2 b extracts the translation parameter(s) IP address fromthe SIP message (invite) and sends an address query request 600including the translation parameter(s) IP address to the addresstranslation unit 1 b (254).

The unit 1 b makes a search through the translation information table500 of the translation entry creation processing part 12 using thetranslation parameter(s) IP address.

If the IP address is absent from the table 500 of the processing part12, the translation unit 1 b creates a translation entry. The unit 1 bassigns an IPv4 private address as a temporary IPv4 addresscorresponding to the IPv6 address. The unit 1 b sets the translationentry to the table 500 of the translation information memory part 16(255).

The address translation unit 1 b sends an address query request response650 to the gateway 2 b (256). A value indicating the IPv4 privateaddress is set to the IP address type (response) field 623 of theresponse 650.

The gateway 2 b translates IP address information in the SIP message.The gateway 2 b translates the translation parameter(s) IP address intoan IP address (IPv4 private address) after translation and an IPv4global address assigned to the IPv4 interface of the translation unit 1b.

Having received the SIP message (invite) from the gateway 2 b (257), thetranslation unit 1 b translates address information of the IP header ofa packet containing the SIP message (258). Referring to the table 500 ofthe translation information memory part 16, the translation unit 1 btranslates the destination address into the real IPv4 address of the SIPserver 5 c and the source address into the temporary IPv4 address of theSIP server 5 b.

FIG. 36 shows a message example 408 of the SIP message (invite) from theaddress translation unit 1 b to the SIP server 5 c.

The temporary IPv4 address (vpmn4) and the IPv4 global address (trbg4)are set to a via header, a call-ID header, a contact header field, and ac field.

The SIP server 5 c receives the SIP message (invite; 259), determinesthe location of the terminal 4, and sends the message to the terminal 4(260).

If the SIP message (invite) is acceptable, the terminal 4 sends a SIPmessage (200 OK) as a response.

The terminal 4 acquires the address (vpmn4) of the mobile node 3 and theIPv4 global address (trbg4) of the address translation unit 1 b from thec field of the message (invite) to use the information to send a packetto the mobile node 3. The address vpmn4 is a temporary IPv4 privateaddress corresponding to the home address (mn6) dynamically assigned tothe mobile node 3.

The SIP message (200 OK) is sent to the mobile node 3 via the serverhaving processed the SIP message (invite; 261-266).

The mobile node 3 acquires the temporary IPv6 address (va6) of theterminal 4 from the parameters of the SIP message (200 OK).

Having received the SIP message (200 OK), the mobile node 3 sends aresponse confirmation message (ACK) to the terminal 4 (267-272).

The procedure resultantly sets a logical connection between the mobilenode 3 and the terminal 4, that is, the mobile node 3 and the terminal 4can communicate with each other.

To send a data packet to the terminal 4, the mobile node 3 sets thetemporary IPv6 address (va6) to the destination address. To the sourceaddress, the mobile node 3 sets the home address (mn6) dynamically setto the mobile node 3 (273).

Having received the packet addressed to the temporary IPv6 address (va6)of the terminal 4, the address translation unit 1 b refers to thetranslation entry to translate information of the header (274). Thetranslation unit 1 b sets the IPv4 address (a4) of the terminal 4 to thedestination address and the temporary IPv4 private address (vpmn4) ofthe mobile node 3 to the source address.

Before transferring the data packet to the IPv4 network, the translationunit 1 b of the fourth embodiment encapsulates the packet with thetranslated IP header according to IPv4 (275). The unit 1 b sets the IPv4address (a4) of the terminal 4 to the destination address of theencapsulation header and the IPv4 global address (trbg4) of the unit 1 bto the source address of the encapsulation header (276).

Having received the encapsulated data packet, the terminal 4decapsulates the packet to process the original packet.

FIG. 37 shows a packet transmitting procedure when the mobile node 3identifies the terminal 4 by a fully qualified domain name (FQDN).

The mobile node 3 sends a DNS query request including the FQDN of theterminal 4 to the DNS server 6 b (281). The DNS server 6 b resolves thename of the terminal 4 in corporation with the gateway (DNS-ALG) 9 b andthe DNS server 6 c (282-284, 288).

Using translation information of the translation unit 1 b, the gateway 9b translates the IPv4 address (a4) for the FQDN of the terminal 4 intothe temporary IPv6 address (va6; 285-287). The translation informationis stored in the translation information table 500 of the translationinformation memory part 16 of the translation unit 1 b.

The mobile node 3 acquires the temporary IPv6 address (va6) as the IPaddress of the terminal 4 (289).

The mobile node 3 sends a packet to the terminal 4 (290). The mobilenode 3 sets the temporary IPv6 address (va6) of the terminal 4 to thedestination address of the packet to the terminal 4 and the home address(mn6) dynamically assigned to the mobile node 3 to the source address ofthe packet.

Having received the packet transmitted to the temporary IPv6 address(va6) of the terminal 4, the address translation unit 1 b translatesinformation of the header according to the translation entry (291). Theunit 1 b sets the IPv4 address (a4) of the terminal 4 to the destinationaddress. The translation unit 1 b assigns an IPv4 private address(vpmn4) as the temporary IPv4 address corresponding to the sourceaddress (mn6) and stores the address in the translation informationtable 500 of the translation information memory part 16.

Before transferring the data packet to the IPv4 network, the translationunit 1 b of the fourth embodiment encapsulates the packet with thetranslated IP header according to IPv4 (292). The unit 1 b sets the IPv4address (a4) of the terminal 4 to the destination address of theencapsulation header and the IPv4 global address (trbg4) of the unit 1 bto the source address of the encapsulation header (293).

Having received the encapsulated data packet, the terminal 4decapsulates the packet to process the original packet.

In the fourth embodiment of the present invention, the addresstranslation unit 1 includes (1) the IPv4 private address pool, (2) theunit to encapsulate by the IPv4 header the packet addressed to the IPv4network, and (3) the unit to notify the address of the translation unit1 to a node existing on the IPv4 network.

Therefore, the translation unit 1 can set an IPv4 private address as atemporary IPv4 address corresponding to an IPv6 node. Even the number ofmobile nodes of the mobile IPv6 to communicate with the IPv4 terminalincreases, the address translation unit can create a translation entryfor the translation from an IPv6 address to an IPv4 address. Thisremoves the problem of insufficient temporary IPv4 addresses of theaddress translation unit in the IPv6-IPv4 address translation.

Description will now be given of a fifth embodiment of the presentinvention. According to this embodiment, in the communication networkshown in the first to fourth embodiments, when the address translationunit 1 receives a control signal or message (Binding Update) requestingregistration of a location from the mobile IPv6 terminal (MN) 3 having ahome address acquired in advance, the translation unit 1 creates atranslation entry in the translation information table 500 of thetranslation unit 1.

The fifth embodiment differs from the first to fourth embodiments in anevent for the mobile node 3 to create the translation entry.

As can be seen from the embodiments of the present invention, theaddress translation unit 1 includes a function to process the mobileIPv6 protocol and the mobile node (MN) 3 conforming to the mobile IPv6includes a function to dynamically acquire a home address and a functionto register a location to the SIP server. When a SIP identifier isassigned to the mobile node 3 and a correspondence between the SIPidentifier of the mobile node 3 and the home address dynamicallyacquired is registered to the SIP server, a packet can be delivered tothe mobile node 3 not having a home address.

The packet addressed to the mobile node 3 passes through the addresstranslation unit 1 existing on the network on which the mobile node 3has dynamically acquired the home address. In communication between amobile node 3 and a terminal 4 existing in mutually different regions ordomains, the route of the packet from the terminal 4 to the mobile node3 can be optimized. By using the session control procedure between themobile node 3 and the terminal 4, audio signals can also be communicatedtherebetween.

The address translation unit 1 includes an IPv4 private address pool, aunit to encapsulate by the IPv4 a packet addressed to an IPv4 network, aunit to decapsulate an encapsulated packet received from the IPv4network, a unit to notify the address of the translation unit 1 to anode existing on the IPv4 network. The translation unit 1 assigns anIPv4 private address as a temporary IPv4 address corresponding to anIPv6 node. This enlarges the address pool of the temporary IPv4addresses to be assigned to mobile nodes 3 by the translation unit 1.Therefore, the communication service can be provided even when thenumber of mobile nodes 3 to communicate with terminals in regions otherthan those of the mobile node 3 is increased.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. An address translation method implemented in an address translator,the address translator connecting a first network conforming to a firstprotocol, a second network conforming to a second protocol, and a mobileterminal in the first network, the mobile terminal having a visitednetwork address used in a visited network and a home network addressused in a home network, the method comprising the steps of: storinginformation of a correspondence between a visited network address of themobile terminal conforming to the first protocol and a home network ofthe mobile terminal conforming to the first protocol, and translationinformation between the home network address of the mobile terminalconforming to the first protocol and a home network address of themobile terminal conforming to the second protocol, translating anaddress in a packet received from another terminal in the second networkfrom the second protocol to the first protocol based on the translationinformation, determining the visited network address of the mobileterminal that uses the translated address as the home network addressconforming to the first protocol; and transmitting the received packetwith the visited network address as a destination address to the mobileterminal; wherein the home network address of the mobile terminalconforming to the second protocol is assigned corresponding to the homenetwork address of the mobile terminal conforming to the first protocoland a correspondence between the assigned home network address of themobile terminal conforming to the first protocol and the home networkaddress of the mobile terminal conforming to the, second protocol isregistered as the translation information when the home network addressof the mobile terminal included in a response to a request forconnecting to the mobile terminal from another terminal passing throughthe address translator is an address conforming to the first protocol.2. The address translation method according to claim 1 furthercomprising a step of. making the translation information using theinformation of a correspondence between an identifier of the mobileterminal and the home network address of the mobile terminal conformingto the first protocol, the information of the correspondence is receivedfrom the mobile terminal.
 3. The address translation method according toclaim 1, wherein the first protocol is IPv6 and the second protocol isIPv4.
 4. The address translation method according to claim 1, whereinthe home network address is a home address of Mobile IP and the visitednetwork address is a care-of address of Mobile IP.